.TH std::nested_exception 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::nested_exception \- std::nested_exception

.SH Synopsis
   Defined in header <exception>
   class nested_exception;        \fI(since C++11)\fP

   std::nested_exception is a polymorphic mixin class which can capture and store the
   current exception, making it possible to nest exceptions of arbitrary types within
   each other.

.SH Member functions

   constructor    constructs a nested_exception
                  \fI(public member function)\fP
   destructor     destructs a nested exception
   \fB[virtual]\fP      \fI(virtual public member function)\fP
   operator=      replaces the contents of a nested_exception
                  \fI(public member function)\fP
   rethrow_nested throws the stored exception
                  \fI(public member function)\fP
   nested_ptr     obtains a pointer to the stored exception
                  \fI(public member function)\fP

.SH Non-member functions

   throw_with_nested throws its argument with std::nested_exception mixed in
   \fI(C++11)\fP           \fI(function template)\fP
   rethrow_if_nested throws the exception from a std::nested_exception
   \fI(C++11)\fP           \fI(function template)\fP

.SH Example



   Demonstrates construction and recursion through a nested exception object.


// Run this code

 #include <exception>
 #include <fstream>
 #include <iostream>
 #include <stdexcept>
 #include <string>

 // prints the explanatory string of an exception. If the exception is nested,
 // recurses to print the explanatory of the exception it holds
 void print_exception(const std::exception& e, int level =  0)
 {
     std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\\n';
     try
     {
         std::rethrow_if_nested(e);
     }
     catch (const std::exception& nestedException)
     {
         print_exception(nestedException, level + 1);
     }
     catch (...) {}
 }

 // sample function that catches an exception and wraps it in a nested exception
 void open_file(const std::string& s)
 {
     try
     {
         std::ifstream file(s);
         file.exceptions(std::ios_base::failbit);
     }
     catch (...)
     {
         std::throw_with_nested(std::runtime_error("Couldn't open " + s));
     }
 }

 // sample function that catches an exception and wraps it in a nested exception
 void run()
 {
     try
     {
         open_file("nonexistent.file");
     }
     catch (...)
     {
         std::throw_with_nested(std::runtime_error("run() failed"));
     }
 }

 // runs the sample function above and prints the caught exception
 int main()
 {
     try
     {
         run();
     }
     catch (const std::exception& e)
     {
         print_exception(e);
     }
 }

.SH Possible output:

 exception: run() failed
  exception: Couldn't open nonexistent.file
   exception: basic_ios::clear

.SH See also

   exception_ptr     shared pointer type for handling exception objects
   \fI(C++11)\fP           \fI(typedef)\fP
   throw_with_nested throws its argument with std::nested_exception mixed in
   \fI(C++11)\fP           \fI(function template)\fP
   rethrow_if_nested throws the exception from a std::nested_exception
   \fI(C++11)\fP           \fI(function template)\fP
